I have sold a Wii U game code for the console's online store back in May. The buyer bought the code, and we've exchanged emails to confirm that the code worked for him.

He had confirmed so that it worked, then a month later he opened a dispute claiming it was an unauthorized payment. He unfortunately won the case, despite the proof I have given Paypal and I had to pay a 20 dollar fee penalty and the money he spent.

So not only is the item his forever (and irreversibly so), but he now has his money back and with me in the red for my paypal balance.